Public transportation is used daily by millions of people in a number of countries, including the United States. As part of this effort to move a lot of people from one place to another in an efficient manner, buses and trains have evolved to operate in a way that decreases fuel consumption, decreases individual man hours, increases safety considerations, and provides for the maximum amount of mechanical operation.
Public transportation has evolved to create entry ways where passengers can enter and exit the vehicle quickly and efficiently. As part of this design effort, exit and entry doors are made larger or multiple doors are used to protect and make accessible one large entry or exit way.
As public transportation expands out into already built-up areas, such as cities, the buses and trains must be flexible. For example, the doors must slide from side to side, as opposed to opening outward or opening inward inside the passenger compartment, so that they can open anywhere there are tight spaces or crowded buses and trains. These buses and trains have an outer shell that is exposed to the elements and an inner shell or inner passenger compartment where passengers and their various items, such as bikes, wheelchairs, bags, computers and service animals, reside while the train or bus travels its route. The outer shell is usually metal or a metal composite that is lined with the material used for the inner passenger compartment, which is usually a polymer-based material, especially in newer trains and buses. For older models, the inside of the train or bus may also be a metal shell.
In some buses and trains, such as those in the SEPTA system in Philadelphia, the doors slide into the shell of the train or bus—the invisible door that slides between panels. However, this design isn't always desirable or feasible in newer trains. These new trains are designed to have thinner shells and be lighter overall to save energy and overall costs.
If the shell of the train or bus is too thin to allow the doors to side into the shell cavity between the panels, then the doors must either move out from the outer shell or move into the inner cavity and slide either right or left to expose the entryway. It is unlikely that these doors would move into the inner cavity where passengers are, because it could be a safety hazard for those passengers. Also, most buses and trains are designed to allow passengers to store bicycles and wheelchairs by the door, so doors sliding into the passenger space would not be a suitable design.
Therefore, the modern design choice for doors on public transportation is for the doors 110 to pop out and away from the shell and the inner passenger cavity, and then to slide along 120 the outer shell of the bus or train to expose or open the entryway 130, as shown in FIG. 1. The doors that are designed this way usually have a track and related wiring at the top of the entryway, as shown in FIG. 2, so that the door moves along the track 240. However, when the door is full open, it is really only secured or anchored on one end. The other end is essentially exposed and not anchored or secured to the train or bus.
In the areas where the buses or trains traverse areas that are on inclines, declines or a mixture of the two, such as San Francisco, these doors open and they are likely going to swing away from the train. Not only can this create a safety hazard in tight places, but it can also put a significant strain on the operating wiring 210 and mechanisms 220 for the door/doors 230, as shown in FIG. 2. This stress or strain not only means that the train or bus will need more routine maintenance, which drives up cost, but it also means that these doors may fail from time to time, which could present a significant safety issue. A terrific example of the problems with train and bus doors is shown in the following video: http://youtu.be/XaZ77kwvSO8.
Therefore, appreciating that modern trains and buses are likely going to continue being designed with doors that pop out and slide either to the right or to the left outside of the train, it would be ideal to design a kit to allow the door to be guided and stabilized outside the train. For brand new trains and buses, they could be initially designed with extra stabilization built into the design without the need of a kit.